1. Field of the Invention
The present invention relates to a driving control circuit of a hood motor, and more particularly to a driving control circuit of a hood motor for controlling rotational speeds of the hood motor.
2. Description of the Related Art
Generally, a hood motor ventilates heat generated under a microwave oven installed over the range (hereinafter called OTR microwave oven), and the smell of foods cooked by the range. The OTR microwave oven having the hood motor is usually installed over a gas range, performing not only a basic function thereof, i.e., the cooking function using microwaves, but also a ventilating function for venting smoke generated during the cooking operation of the gas range.
FIG. 1 is a view for showing a conventional OTR microwave oven installed, and FIG. 2 is a view for schematically showing the inner portion of the OTR microwave oven.
As shown in FIG. 1, the OTR microwave oven includes a body 10 having a cooking chamber 11 therein. On a lower side of the cooking chamber 11, a hood lamp 12 is disposed, while vent ducts 14 are disposed on the left and right sides of the cooking chamber 11.
Further, a hood motor M is installed at the middle rear portion of the cooking chamber 11, and vent blowers 18 are disposed on the left and right sides of the hood motor M. Upper portions of the vent blowers 18 are connected with a connective tube 20, and a vent passage 22.
Accordingly, vapor or smoke generated during the cooking operation of the gas range are drawn into the vent ducts 14 by the rotation of the vent blowers 18, and are exhausted outside through the connective tube 20 and the vent passage.
FIG. 3 is a view for showing the rotational velocity control circuit of the hood motor shown in FIG. 2.
As shown in FIG. 3, the conventional rotational velocity control circuit of the hood motor includes a power on/off switch 330, a rotational velocity selecting switch 332, a temperature sensor 334, and a hood motor M.
The rotational velocity selecting switch 332 selects the rotational velocity of the hood motor M, while being selectively switched on to a low-velocity contact L for selecting the low velocity mode, or to a high-velocity contact H for selecting the high velocity mode.
The hood motor M includes an alternating current (hereinafter called AC) motor selectively rotated at a low or a high velocity in accordance with the selected mode of the low/high velocity contacts L or H.
The temperature sensor 334 senses the temperature of a driving coil in the hood motor M, and has increasing resistance value corresponding to the rise in temperature.
Meanwhile, the presence of foreign substances in the vent blowers 18 of the hood motor M causes a constraint on the rotation of the hood motor M, and accordingly, the temperature of the driving coil is excessively increased. As a result, the resistance value of the temperature sensor 334 is significantly increased, cutting off the application of AC power to the hood motor M.
The conventional control circuit for controlling the rotational velocity of the hood motor M, however, has shortcomings of high manufacturing cost and a low productivity due to its expensive AC motor and temperature sensor.
Further, in the conventional hood motor control circuit, since the low/high velocity contacts of the rotational velocity selecting switch are formed to be mechanically switched on/off to control the rotational velocity of the hood motor M, there is a high possibility of having poor contacts due to frequent switching, and the danger of fire due to spark at the contacts.